Saturday, May 12, 2012

Final Exam Review Time!

Question: What makes a bond polar? What makes a molecule polar? How does this compare to ionic bonds? Please give examples of each.

Answer:

Polarity can be very confusing if not fully understood. Polarity can occur in three ways, Polar Covalent Bonds, Dipoles, and the Bond Continuum. What makes bonds polar is a difference in electronegativity of atoms. The electronegativity of an atom is the ability of that atom to attract electrons in a bond. Given this definition the more electronegative the atom, the more it will keep its electrons to itself and will not "share" them with other atoms and vice versa. If one atom is more electronegative than the other, the more electronegative atom will hog the electrons of the other atom for itself, creating a slightly more negative side of the bond. An example of this Polar Covalent Bond is the acid bond of HCl. The electronegativity of Hydrogen is about 2.1 while that of Chlorine is about 3. The chlorine atom naturally pulls the Hydrogen's electrons towards itself, which creates a greater concentration of electrons around the chlorine atom which means there is a slight negative charge on the chlorine and a slight positive charge on the hydrogen. The Bond Continuum occurs when a covalent bond becomes too polar. When this happens, the more electronegative atom will actually steal the electron from the other atom, thus essentially turning into an ionic bond. Polarity in covalent compounds also creates dipoles. Dipoles are two electronegative poles, like in the world, of a bond, one positive and one negative. When polar bonds combine in molecules with multiple bonds and at least two sigma bonds, an overall polarity can occur. An example of this is water, H2O, in which the Oxygen atom, being more electronegative, draws the Hydrogens' two electrons towards it, creating a positive side where the hydrogens are and a negative where the oxygen is due the the increased/decreased electrons there.

1 comment:

Great post, Nicole! Your answers were very thorough and clearly explained. The only two things that I would add to make your post more clear are: 1.) The HCl molecule is polar because some of its the hydrogen's electrons have been transferred to the chlorine atoms – causing it to have a slightly positive charge due to the missing electrons. And, 2.) Polarity within a molecule causes other molecules around it to form in a certain way that is compatible with the polarity of the first molecule. Other than the addition of those two things, your post is great and does an excellent job of explaining polarity.